OPERATION
PTC thermistors exhibit very high sensitivity over a
narrow temperature band. For temperature measure-
ment in this range, NTC thermistors are easier to
measure and more accurate.
- PTC’s are classified according to their nominal
response temperature
NAT
but all have similar
resistance characteristics to simplify the choice
of switching device; the relationship of resistance
to temperature of all these PTC’s is as follows:
STANDARD RESISTANCE VALUES
Single PTC
Temperature
Resistance
measuring Voltage
°C
V
– 20 to
NAT
– 20
250 max./100 max.
2.5
NAT
– 5
550 max.
2.5
NAT
1.000
2.5
NAT
+ 5
1.330 min.
2.5
NAT
+ 15
4.000 min
7.5
PTC thermistors are especially suited as temperature
sensors for monitoring the windings of electric
machines, and also for use in simple fail-safe circuitry.
When a given temperature (nominal response tempe-
rature
NAT
) is exceeded, the circuit can be switched
off through a relay or amplifier, since the PTC-sensor
will have an extremely high ohmic value in the region
of its response temperature. This will have the same
effect as a break in the circuit or a failure of the
thermistor.
TECHNICAL DATA
Nominal response temperature
80 ° to 180 °C in steps
of 10 °, plus 145 ° and 155 °C
Maximum allowable operating temp.
Tmax. 200 °C
Max. allowable operating voltage at + 25 °C
Umax. 25V (per bead)
Max. allowable power dissipation at + 25 °C
690 mW
Insulation strength (between leads and outer insulation)
also for threaded sensor
2.5 kV
Conductors - silvered copper wire with teflon insulation
PTFE
Insulation stripping
approx 10 mm
Conductor cross-section
0.25 mm2 for single, double
and triple PTC’s
CONDUCTOR LENGTHS
Single PTC
500 mm
10 mm
Double PTC
500 - 180 - 500 m
10 mm
Triple PTC
500 - 180 - 180 - 500 mm
10 mm
SPECIAL VERSIONS
PTC’s are also available in many special housings
(can be manufactured to customers specifications)
INSTALLATION TIPS
For PTC temperature sensors in electrical windings:
- the thermistors can only be inserted in the windings
before impregnation
- it is advisable to embed one in each phase, if
possible in the centre of the coil generating most
heat, and generally on the outflow side of any air
movement
- air inflow onto the temperature sensor will interfere
with heat transfer
- if using varnish/lacquer which is not chemically
neutral, suitability tests must be undertaken by the
customer
- WARNING! It is very important that the sensor must
be installed parallel with the copper of the winding,
so that the teflon leads can assume the form of the
rest of the winding and thereby retain the high-
voltage resistance rating.
Triple PTC
Temperature
Resistance
measuring Voltage
°C
V
– 20 to
NAT
– 20
750 max./300 max.
7.5
NAT
– 5
1.650 max.
7.5
NAT
+ 5
4.000 min.
7.5
NAT
+ 15
4.000 min.*
7.5
* one PTC might reach
NAT
+ 15 °C, while the second or even both
of the others could still remain at room temperature.
The PTC’s resistance values for motor protection are
specified in DIN 44081/44082. Resistance values
below
NAT
–20 are not specified, and resistance
when cold is no indication of the PTC’s condition. It is
ideally between 40 - 200 ohms but can be anywhere
between 35 - 250 ohms.
The greatest resistance change occurs between
5 °C either side of
NAT
, being at least 15%/K.
Twin/double and triple PTC’s are available with
standard or mini-bead.
QUALITY STANDARD
Random testing is carried out according to DGQ
P90/P10 (DIN 40080). AQL values can be fixed by
arrangement.
ORDERING INFORMATION
Quantity
Type
Temperature
Resistance
code No.
max.
1.000
YD1
C 510
250 ohms
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